Myelin mapping in the central nervous system of living mice using contrast-enhanced magnetization transfer MRI.
This work compares magnetization transfer (MT) MRI of living mice with contrast-enhanced MT MRI using intraventricular administration of gadopentetate dimeglumine (Gd-DTPA), systemic administration of MnCl(2), and both. In MT MRI at 9.4T, the contrast-to-noise ratio (CNR) between white matter (WM) and gray matter (GM) increased by 85% after Gd-DTPA injection into the lateral ventricle. When applied in conjunction with manganese-enhanced MT MRI (117μm isotropic resolution, 6min measuring time), Gd-DTPA boosted the CNR increase from +56% to +117%. Additional T(1) measurements at 2.35T revealed that intraventricular Gd-DTPA shortens the T(1) of GM much more than that of WM, which corresponds to estimated extracellular spaces of 26% in GM and only 15% in WM. These results explain the additional MT contrast enhancement by Gd-DTPA and demonstrate that the T(1) shortening by intracellular Mn(2+) is well complemented by extracellular Gd-DTPA. The data suggest a high myelin and low water content to hinder access of hydrophilic paramagnetic agents, so that the resulting differential accumulation effectively reduces the MT saturation in water-rich tissues and thereby facilitates the mapping of myelin-rich tissues. Finally, a 156% CNR increase between GM and WM for contrast-enhanced MT MRI at 9.4T using both Gd-DTPA and manganese allowed for 60μm isotropic resolution (102min measuring time), which delineated myelinated fibers and layers even within GM areas such as the thalamus and cerebellar cortex. Improved MT contrasts were also seen in the cervical spinal cord.[1]References
- Myelin mapping in the central nervous system of living mice using contrast-enhanced magnetization transfer MRI. Watanabe, T., Frahm, J., Michaelis, T. Neuroimage (2012) [Pubmed]
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